Engineering of a functional tendon

Reconstruction of a tendon following rupture is surgically challenging as each end of the tendon retracts leaving a substantial gap so that direct repair is often not feasible. To restore function, a tendon graft is required to bridge this defect and presently these gaps are filled with auto-, allo- or, synthetic grafts but they all have clinical limitations. To overcome this problem, tissue engineered collagen grafts were developed by a rapid process using compressed cell seeded type I collagen. Previously these constructs were tested in vivo in intercostal spaces of a lapine model to test immunocompatibility but material properties of the tissue engineered collagen grafts are currently unsuitable to withstand complete load bearing in vivo. A modified suture technique was developed to physiologically withstand and off load the tissue engineered collagen graft to aid integration in vivo. This modified suture method allowed only partial load to be transferred onto the tissue engineered collagen graft. Lapine tendons were used to test mechanical strength of repairs and a stress model was built. The break point for modified suture technique with tissue engineered collagen graft in situ was significantly higher compared to standard modified Kessler suture technique. To test the effect of the partial load on tenocytes, mechanobiology was studied under static and 10% cyclic loads using custom designed tensioning culture force monitors with immunohistology and matrix remodelling gene expression as quantifiable outcomes. Tendon fibroblast seeded tissue engineered collagen grafts were tested in vivo in a lapine model up to 12 weeks without immobilization. The gross observation at 3 and 12 weeks showed bridged integration of the graft without any adhesion with significant increase in the mechanical properties for 3 and 12 weeks as compared to 1 week. Histological analysis showed that tendon fibroblasts from the native tendon were able to migrate into the graft with higher collagen remodelling and graft maturation at 12 weeks as compared to 3 and 1 week. Insertion of tissue engineered collagen graft using a novel load bearing suture technique which partially loads in vivo showed integration, greater mechanical strength and no adhesion formation in the time period tested and it has inherent advantages as compared to the present day tendon grafts.